EGR ratio from exhaust gas composition

[mrcarbon4hydrohen]

Homework Statement

given:-fuel and air mass flow, measured mole ratios of exhaust composition y_i. Let's assume stoichiometric combustion so we have only CO2, H20 and N2 as products.

Homework Equations

Can EGR ratio be calculated from available data?

The Attempt at a Solution

I get result that molar ratios don't depend on EGR ratio.

 

[Chestermiller]

Your first equation already tells you this.

 

[mrcarbon4hydrohen]

I have another question. I there is excess air, can EGR be determined? Folowing the same logic as before, it can't. This time I used a slightly different formula but result is the same.

but..
I found a SAE paper in which (Fresh Air+EGR)/Fuel ratio is determined by exhaust concentrations. So I think there is connection between EGR and gas concentations in exhaust. This is the paper(you can see in preview of SAE paper what I am referring to, equation (3)): http://papers.sae.org/2010-01-1285/ .I tried to get solution as in paper, but got different result.

 

[Chestermiller]

As best I can tell, the mole fractions of the gases in the exhaust are independent of the recycle ratio.